Re: [PATCH v4 1/2] xen/arm: exclude xen,reg from direct-map domU extended regions

["Orzel, Michal" <michal.orzel@xxxxxxx>]

On 09/06/2025 20:34, Stewart Hildebrand wrote:
> Similarly to fba1b0974dd8, when a device is passed through to a
> direct-map dom0less domU, the xen,reg ranges may overlap with the
> extended regions. Remove xen,reg from direct-map domU extended regions.
> 
> Take the opportunity to update the comment ahead of find_memory_holes().
> 
> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
> ---
> v3->v4:
> * conditionally allocate xen_reg
> * use rangeset_report_ranges()
> * make find_unallocated_memory() cope with NULL entry
> 
> v2->v3:
> * new patch
> ---
>  xen/arch/arm/domain_build.c           | 77 +++++++++++++++++++++++++--
>  xen/common/device-tree/domain-build.c |  5 ++
>  2 files changed, 77 insertions(+), 5 deletions(-)
> 
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index 590f38e52053..6632191cf602 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -792,15 +792,17 @@ static int __init handle_pci_range(const struct 
> dt_device_node *dev,
>  }
>  
>  /*
> - * Find the holes in the Host DT which can be exposed to Dom0 as extended
> - * regions for the special memory mappings. In order to calculate regions
> - * we exclude every addressable memory region described by "reg" and "ranges"
> - * properties from the maximum possible addressable physical memory range:
> + * Find the holes in the Host DT which can be exposed to Dom0 or a direct-map
> + * domU as extended regions for the special memory mappings. In order to
> + * calculate regions we exclude every addressable memory region described by
> + * "reg" and "ranges" properties from the maximum possible addressable 
> physical
> + * memory range:
>   * - MMIO
>   * - Host RAM
>   * - PCI aperture
>   * - Static shared memory regions, which are described by special property
>   *   "xen,shared-mem"
> + * - xen,reg mappings
>   */
>  static int __init find_memory_holes(const struct kernel_info *kinfo,
>                                      struct membanks *ext_regions)
> @@ -882,6 +884,13 @@ static int __init find_memory_holes(const struct 
> kernel_info *kinfo,
>          }
>      }
>  
> +    if ( kinfo->xen_reg_assigned )
> +    {
> +        res = rangeset_subtract(mem_holes, kinfo->xen_reg_assigned);
> +        if ( res )
> +            goto out;
> +    }
> +
>      start = 0;
>      end = (1ULL << p2m_ipa_bits) - 1;
>      res = rangeset_report_ranges(mem_holes, PFN_DOWN(start), PFN_DOWN(end),
> @@ -962,11 +971,48 @@ static int __init find_domU_holes(const struct 
> kernel_info *kinfo,
>      return res;
>  }
>  
> +static int __init count(unsigned long s, unsigned long e, void *data)
> +{
> +    unsigned int *cnt = data;
> +
> +    (*cnt)++;
> +
> +    return 0;
> +}
> +
> +static int __init rangeset_to_membank(unsigned long s_gfn, unsigned long 
> e_gfn,
> +                                      void *data)
> +{
> +    struct membanks *membank = data;
> +    paddr_t s = pfn_to_paddr(s_gfn);
> +    paddr_t e = pfn_to_paddr(e_gfn + 1) - 1;
Why do you subtract 1 here if ...

> +
> +    if ( membank->nr_banks >= membank->max_banks )
> +        return 0;
> +
> +    membank->bank[membank->nr_banks].start = s;
> +    membank->bank[membank->nr_banks].size = e - s + 1;
you add it again here.

> +    membank->nr_banks++;
> +
> +    return 0;
> +}
> +
>  static int __init find_host_extended_regions(const struct kernel_info *kinfo,
>                                               struct membanks *ext_regions)
>  {
>      int res;
>      struct membanks *gnttab = membanks_xzalloc(1, MEMORY);
> +    struct membanks *xen_reg =
> +        kinfo->xen_reg_assigned
> +        ? ({
> +            unsigned int xen_reg_cnt = 0;
> +
> +            rangeset_report_ranges(kinfo->xen_reg_assigned, 0,
> +                                   PFN_DOWN((1ULL << p2m_ipa_bits) - 1), 
> count,
> +                                   &xen_reg_cnt);
This does not look really nice with ({. Why can't we create a helper function to
report the count for xen_reg_assigned and call it here? You could then also open
code your 'count' function that is not used by anything else and is quite 
ambiguous.

~Michal

> +            membanks_xzalloc(xen_reg_cnt, MEMORY);
> +          })
> +        : NULL;
>  
>      /*
>       * Exclude the following regions:
> @@ -974,6 +1020,7 @@ static int __init find_host_extended_regions(const 
> struct kernel_info *kinfo,
>       * 2) Remove reserved memory
>       * 3) Grant table assigned to domain
>       * 4) Remove static shared memory (when the feature is enabled)
> +     * 5) Remove xen,reg
>       */
>      const struct membanks *mem_banks[] = {
>          kernel_info_get_mem_const(kinfo),
> @@ -982,12 +1029,29 @@ static int __init find_host_extended_regions(const 
> struct kernel_info *kinfo,
>  #ifdef CONFIG_STATIC_SHM
>          bootinfo_get_shmem(),
>  #endif
> +        xen_reg,
>      };
>  
>      dt_dprintk("Find unallocated memory for extended regions\n");
>  
>      if ( !gnttab )
> -        return -ENOMEM;
> +    {
> +        res = -ENOMEM;
> +        goto out;
> +    }
> +
> +    if ( kinfo->xen_reg_assigned )
> +    {
> +        if ( !xen_reg )
> +        {
> +            res = -ENOMEM;
> +            goto out;
> +        }
> +
> +        rangeset_report_ranges(kinfo->xen_reg_assigned, 0,
> +                               PFN_DOWN((1ULL << p2m_ipa_bits) - 1),
> +                               rangeset_to_membank, xen_reg);
> +    }
>  
>      gnttab->nr_banks = 1;
>      gnttab->bank[0].start = kinfo->gnttab_start;
> @@ -995,6 +1059,9 @@ static int __init find_host_extended_regions(const 
> struct kernel_info *kinfo,
>  
>      res = find_unallocated_memory(kinfo, mem_banks, ARRAY_SIZE(mem_banks),
>                                    ext_regions, add_ext_regions);
> +
> + out:
> +    xfree(xen_reg);
>      xfree(gnttab);
>  
>      return res;
> diff --git a/xen/common/device-tree/domain-build.c 
> b/xen/common/device-tree/domain-build.c
> index 6b8b8d7cacb6..99ea81198a76 100644
> --- a/xen/common/device-tree/domain-build.c
> +++ b/xen/common/device-tree/domain-build.c
> @@ -193,6 +193,10 @@ int __init find_unallocated_memory(const struct 
> kernel_info *kinfo,
>  
>      /* Remove all regions listed in mem_banks */
>      for ( i = 0; i < nr_mem_banks; i++ )
> +    {
> +        if ( !mem_banks[i] )
> +            continue;
> +
>          for ( j = 0; j < mem_banks[i]->nr_banks; j++ )
>          {
>              start = mem_banks[i]->bank[j].start;
> @@ -212,6 +216,7 @@ int __init find_unallocated_memory(const struct 
> kernel_info *kinfo,
>                  goto out;
>              }
>          }
> +    }
>  
>      start = 0;
>      end = (1ULL << p2m_ipa_bits) - 1;